The fix is easy enough though... you can confirm that the filter has reliably solved your issues for the long-term?

Thanks!

Good guess, and I am sorry to say so, but it does not reliably solve the issue.
It works for a test slope around the block with cold engine and low revs. As soon as revs go up and throttle goes up values will get garbled as always. The main factor seems to be riding speed and throttle status, suprisingly. When going in first gear and with low throttle it will display acurate all the way up it seems.

So, for a calm commute it might work out. For an enduro ride it will definitely not work out at all. I will give up on it now.
That was my last try, I really tried everything on it. The only way to get this going reliably was to disconnect external power completely. And thats no option to me.